Three-dimensional quantification of macropore networks in undisturbed soil cores

The role of macropores in soil and water processes has motivated many researchers to describe their sizes and shapes. Several approaches have been developed to characterize macroporosity, such as the use of tension infiltrometers, breakthrough curve techniques, image-analysis of sections of soils, and CAT scanning. Until now, efforts to describe macropores in quantitative terms have been concentrated on their two-dimensional (2-D) geometry. The objective of this study is to nondestructively quantify the three-dimensional (3-D) properties of soil macropores in four large undisturbed soil columns. The geometry and topology of macropore networks were determined using CAT scanning and 3-D reconstruction techniques. Our results suggest that the numerical density of macropores varies between 13,421 to 23,562 networks/m(3) of sandy loam soil. The majority of the macropore networks had a length of 40 mm, a volume of 60 mm(3), and a wall area of 175 mm(2). It was found that the greater the length of networks, the greater the hydraulic radius. The inclination of the networks ranged from vertical to an angle of approximately equal to 55 degrees from vertical. Results for tortuosity indicated that most macropore networks had a 3-D tortuous length 15% greater than the distance between their extremities. More than 60% of the networks were made up of four branches. For Column 1, it was found that 82% of the networks had zero connectivity. This implies that more than 4/5 of the macropore networks were composed of only one independent path between any two points within the pore space.